This invention relates to an opto-electrical actuation system and method. Specifically, it relates to a system and method in which light is used to selectively actuate and control a plurality of electrical devices. References to actuation herein are intended to include controlling and/or supplying operating power to the devices.
The system and method in accordance with the invention are intended to supply electrical power at an effective actuating voltage selectively to one or more of a plurality of devices. The power may be used to switch the devices, or to supply running power to them, according to the demands of the devices and the availability of other electrical power sources.
The invention is particularly suitable for downhole use at oil and gas exploration and production sites, in environments where temperatures can reach up to 300xc2x0 C.
In accordance with one aspect of the invention, there is provided an actuation system for a plurality of electrically actuated devices, comprising a pulsed light source of variable pulse frequency directed to a plurality of actuation gateways each adapted to supply an electrical actuation voltage above a threshold value to an associated device when illuminated by light pulsed at a trigger frequency for that device.
Each said gateway is suitably provided with an optical sensor such as photovoltaic converter means for converting pulsed incident light to a low voltage pulsed electrical current in the order of 3 to 5 volts, of corresponding frequency. Frequency sensitive ferroelectric DC-DC converter means may be provided for transforming the low voltage of the pulsed current to a higher voltage above the threshold value, typically 600-800 volts, for the associated device when the current frequency is at the trigger frequency. The DC-DC converter means may be a ferroelectric transformer and the trigger frequency is then suitably a resonant frequency of the transformer selectably adjusted by variation in the component geometry. In some embodiments of the invention output voltages for the converter as low as 100 volts may be adequate to activate the associated device.
The trigger frequency may be in a band of not more than about 3 kHz within the range 10 kHz to 40 kHz. The trigger frequencies of ferroelectric transformers to be operated independently are suitably separated to compensate for environmental effects, such as pressure and temperature, by a frequency difference of about 3 kHz or more.
The system desirably includes optical pathway means for directing light from the light source to the plurality of actuation gateways. The optical pathway means may comprise a branched network of optical fibres connected by optical couplers. The coupler splitting ratios may be selected to provide optimum power to the devices to be actuated. Such ratios will depend upon the number of devices on the network and the available light source power. Typical optical coupling splitting ratios are in the order of 5:1 and are so selected as to provide optical power in the order of 40 to 50 mW to the photovoltaic converter. The optical couplers should also be selected from materials suitable for the elevated thermal conditions of the surrounding environment. A sufficient optical power budget should be provided to accommodate changes in splitting ratio and photovoltaic conversion efficiency under the changing environmental conditions.
The invention further provides a method of actuating a plurality of electrical devices which comprises providing an actuating system for the said devices as set out above, and selectively actuating a device by illuminating the actuation gateways with light pulsed at a frequency that corresponds to the trigger frequency of the selected device.